(a) Field of the Invention
The present invention relates to a flow regulating apparatus used for an intravenous infusion set (IV set), and more particularly to, a linear flow regulating apparatus which is capable of linearly regulating the flow rate of an infusion solution.
(b) Description of the Related Art
As shown in FIG. 1, an intravenous injection system for intravenous administration of fluids includes an infusion solution bag 100 containing an infusion solution, an insertion spike 101 adapted to be inserted through a sealing plug of the infusion solution bag 100 to allow the infusion solution to be flown out from the infusion bag 100, a drip chamber 102 fixed to the lower end of the insertion spike 101 so that the infusion solution can fall in drops (counted in a unit of gtt) within the drip chamber 102, an injection needle 103 adapted to be inserted into a vein, a connecting tube 104 for interconnecting the drip chamber 102 and the injection needle 103 to serve as an infusion passage for the infusion solution, and an infusion flow regulator 110 mounted in the middle of the connecting tube 104 to be capable of regulating the flow rate of the infusion solution.
In general, the insertion spike 101, the drip chamber 102, the injection needle 103, the connecting tube 104, and the infusion flow regulator 110 are fabricated in one set, wherein the set fabricated in this manner is referred to as an infusion set. After the infusion solution in the infusion solution bag 100 connected to the infusion set is completely infused to a patient, only the empty infusion bag 100 may be replaced by a new one containing the same infusion solution if it is necessary to continuously inject the infusion solution to the patient. In addition, the insertion spike 101 and the drip chamber 102 are fabricated to make each of the drops of the infusion solution fall within the drip chamber 102 in the form of a water drop with a predetermined volume. For example, if they are fabricated to form 20 drops per 1 cc of the infusion solution, the volume of one drop will be 1/20 cc. Therefore, if the drops' falling interval within the drip chamber 102 is measured, it is possible to calculate the flow rate of the infusion solution injected through the infusion set.
For injecting an infusion solution to a patient, the flow rate of the infusion solution is prescribed in consideration of the type of the infusion solution, the kinds of agents mixed in the infusion solution, the condition of the patient, the kind of the disease of the patient, and the infusion flow regulator 110 is tuned so as to allow the infusion solution to be injected with the prescribed flow rate.
Regulating the flow rate of the infusion solution is very important since a medical accident may occur if the flow rate of the infusion solution being infused is not matched to the prescribed flow rate. Such an infusion flow regulator 110 has a manipulation unit 111 for regulating the cross-sectional area for passage of the infusion solution through the connecting tube 104, so that the flow rate of the infusion solution can be regulated by manipulating the manipulation part 111.
The conventional infusion flow regulator 110 shown in FIG. 2 is a so-called “roller clamp” type infusion regulator, in which the manipulation unit 111 is formed in a roller type. Referring to the infusion flow regulator 110 in more detail, a connecting tube 104 is inserted through a recess 112 having opened top and bottom ends, and then the manipulation unit 111 adapted to press the connecting tube 104 is guided upward and downward. Since the depth of the recess 112 is gradually reduced toward the lower end, and hence the connecting tube 104 is pressed more and more as the manipulation unit 111 is moved more and more to the lower end of the recess 112. Thus, the flow rate of infusion fluid is regulated by measuring the flow rate at plural points while intermittently moving the manipulation unit 111, and by stopping the movement of the manipulation unit 111 when the flow rate reaches a desired level.
However, the roller clamp type infusion flow regulator 110 shown in FIGS. 1 and 2 is disadvantageous in that, since the flow rate should be measured while seeing the drip chamber 102 whenever the roller type manipulation unit 111 is moved, complicated measurements (drip rate counts) should be repeatedly performed, which will deteriorate the accuracy of flow rate regulation.
Moreover, the biggest problem of the conventional roller clamp type infusion flow regulator 110 is that it is difficult to regulate the flow rate. The conventional infusion flow regulator 110 regulates the flow rate by adjusting the flow passage area by pressing the connecting tube 104. Once the connecting tube 104 is pressed, the cross-section of the connecting tube 104 is deformed from a circular shape to an elliptical shape, and the cross-sectional area and the hydraulic radius of the connecting tube 104 become smaller, thus resulting in a flow reduction.
According to the Hagen-Poiseuille equation (Hagen-Poiseuille law in pipe) shown in the following Equation 1, which assumes that a flow in a cylindrical tube is steady and laminar, the velocity profile of a fluid flowing within the tube is parabolic, and the flow rate of the fluid is inversely proportional to the length of the tube and proportional to the fourth power of the radius. This results in nonlinear flow regulation, and therefore it is difficult to accurately regulate the flow rate merely by varying the length or radius of the cylindrical tube.
                    Q        =                                                            Δ                ⁢                                                                  ⁢                p                ⁢                                                                  ⁢                π                ⁢                                                                  ⁢                                  r                  0                  4                                                                                                        8                ⁢                                                                  ⁢                μ                ⁢                                                                  ⁢                1                                                                        Equation        ⁢                                  ⁢        1            
(where Q is the flow rate, r0 is the radius of the tube, l is the length of the tube, μ is the viscosity of the fluid, and Δp is the pressure difference in the tube.)
As above, regulating the flow rate by variations in diameter and length is nonlinear and complex even in the cylindrical tube having quite a simple structure. Moreover, variations in the cross-sectional area and length of the flow passage are even more complicated in the roller clamp type flow regulator, making flow regulation more difficult.
Further, the conventional infusion flow regulator 110 includes the above-mentioned roller clamp type flow regulator, a cylindrical rotary flow regulator, a clock-type flow regulator, a constant infusion pump, etc. Although the roller clamp type flow regulator can vary the flow passage area by a roller, it is not capable of uniformly adjusting the dimension, shape, hydraulic radius, etc of the flow passage area. Therefore, the roller clamp type flow regulator has the drawbacks that it is difficult to regulate the flow rate by the above-mentioned Equation 1, the roller for manipulation is easily moved at a fixed position, and a creep may occur in a deformed tube over time, causing a change in flow rate.
The rotary flow regulator has a constant cross-sectional area, and is adapted to regulate flow rate by adjusting the length (which is proportional to the angle of rotation) of a capillary tube by turning the dial. The rotary flow regulator also has the problem that it is difficult to regulate the flow rate according to the above-mentioned Equation 1 (the scale is nonlinear because the flow rate is inversely proportional to the length l of the capillary).
In addition, the constant infusion pump has the problems that it is not convenient to install and use it due to its large size, and runs a high risk of contamination because it is used on many people.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.